Presently, many electrical power distribution circuits have areas that are supplied with substandard power. This may take the form of voltages being out of tolerance and/or a distribution circuit being overloaded. These problems result from the impedance (real or reactive) between the generating plant and the load being higher than what is desired. If the problem is severe enough, failures in the distribution circuit will occur. Distorted or out-of-tolerance voltages supplied to end-users may also result in end-user equipment over-heating and subsequent failure.
There are several causes of these problems. Additional loads being added to the distribution circuit, or the movement of loads over time, may cause portions of distribution circuit to become overloaded. The tendency for end-user's loads to be inductive, in addition to the natural inductive nature of a typical distribution circuit, can cause significant out-of-phase 60 Hz reactive power to exist in the distribution circuit. This reactive power does not contribute to any real work being performed, but does result in unwanted power losses in the distribution circuit.
Unbalanced loading of the 3 phases of the distribution circuit, caused by single phase loads that are not evenly distributed between the 3 phases, can cause one or more of the phases to be overloaded while the other phase(s) are below capacity. This current imbalance will result in unequal voltages between the phases. In addition, the overloaded phase(s) may eventually cause a failure in the distribution circuit by overheating a component thereof.
Non-linear loads, such as motor drives, computers, fluorescent lighting and the like, draw harmonic currents. The distribution circuit must supply these harmonic currents, which are at higher frequencies such as 180 Hz, 300 Hz, 420 Hz, 540 Hz, 660 Hz, etc. (i.e., odd ordered harmonics of 60 Hz), and again do not contribute to any real work. These higher frequency harmonic currents flowing through the distribution system result in skin effect, proximity effect, and eddy current power losses in components of the distribution circuit. If these harmonic currents exist at significant levels, overheating and failure of one or more components of the distribution circuit can occur. Since the distribution circuit is inductive in nature and the impedance of the distribution circuit increases with increased frequency, there can be significant voltage drops in the circuit that results in distorted voltages. These distorted voltages result in additional heating in some loads, such as AC motors, which could lead to premature failures in such loads.
These problems can be reduced, but not eliminated, by increasing the size of components in the distribution circuit. This, however, is an expensive proposition (in both monetary terms and in terms of increased need for larger components in the distribution circuit), especially if the heavier loads are a significant distance from the generating facility. In such a case, a large portion of the distribution circuit may need to be upgraded. Even with such upgrading, there may still be locations along the distribution circuit that have distorted or substandard voltage levels. Also, future load shifts can occur that can render these improvements suboptimal or obsolete.